Extrusion dies



P. J. NICHOLL 3,298,062

EXTRUSION DIES Jan. 17, 1967 2 Sheets-Sheet l Filed May 4, 1965 P. J. NICHOLL EXTRUSION DIES Jan. 17, 1967 2 Sheets-Sheet 2 Filed May 4, 1965 Q EIIJ INVENTOR. Ev -g Jim/s5 N/(LHOLL ro/W516 United States Patent 3,298,062 EXTRUSIUN DllES Peter James Nicholl, London, England, assignor to Brown and Williamson Tobacco Corporation, Louisville, Ky, a corporation of Delaware Filed May 4, 1965, Ser. No. 453,113 Claims priority, application Great Britain, May 7, 1%4, 19,t}22/ 64 8 Claims. (Cl. 18-12) This invention concerns improvements relating to dies for the extrusion of filaments of plastic materials such as plastics and, in particular, reconstituted tobacco compositions.

It is known to produce filaments from plastics by extruding the material through dies provided with slits or holes which form the filaments. When fine filaments are required, the slits or holes must necessarily be very small and are therefore difficult to produce accurately, especially it extremely hard materials are used for the dies. Also there is considerable risk of blockage of the slits or holes with the result that production has to be stopped and the die removed for cleaning or replacement. Furthermore, if a relatively abrasive material is extruded, the slits or holes rapidly become enlarged, which again necessitates removal and replacement of the die. Since dies for fine filaments are expensive, their continual replacement and the necessity to stop production during replacement adds considerably to the costs of production. Accordingly, the present invention seeks to provide inexpensive and easily producible and replaceable die means for the production of fine filaments of plastic materials.

According to the invention, die slits are formed by serrations at an edge of a thin metal sheet disposed in replaceable manner on one side, suitably the underside, of a die channel to which the material to be extruded is supplied, preferably by way of a plurality of rows or sets of orifices formed in a die bar or block and arranged to open into the said channel, which is provided in one side, suitably the underside, of the said bar or block. If desired, a shallow cavity may be provided over the entry ends of the sets of orifices, to accommodate a filtering screen for the material to be extruded.

One embodiment of the invention, by way of example, will now be more fully described with reference to the accompanying drawings, in which:

FIGURE 1 is an isometric view of a die with parts cut away to disclose underlying components,

FIGURE 2 a detail view to a larger scale showing the die slits,

FIGURE 3 a similar View showing feed ducts, and

FIGURE 4 an exploded longitudinal section of a die head.

In the form of the embodiment illustrated, strips of shim metal 1 and 2 are arranged, edge to edge, under neath and one to each side of a narrow longitudinal die channel 3 in the middle of the underside of a die body 4. The latter is a stiff bar of inverted U-section, closed at the ends, and rests upon a base 5, also in the form of a still bar, which has a slot-shaped filament-guiding chamber 6 extending through the base 5 from top to bot tom. The shim strips 1 and 2 are supported upon bars or plates 7 which in turn rest on the base 5, one on each side of the chamber 6. The bars 7, which may be made of abrasive-resistant material such as hardened steel, have tapered lip portions 7a between whose adjacent edges there is an extrusion slot located underneath the channel 3. One of the shim strips, as shown the strip 1, has a serrated edge 1a (FIGURE 2) which is bent down at right angles so that the toothed portion projects into the said extrusion slot. The other shim strip 2 has a plain edge 2a, abutted against the serrated edge In and acts 3,Z8,%2 Patented Jan. 17, 1967 simply as a distance piece. The shim strips 1 and 2 are held firmly to bars 7 inside the body 4, with the serrated edge In tightly gripped between the lip portions 7a of the bars 7, by a small metal bar 8 which is secured by clamping screws provided at intervals in the said body. The lip portions 7a form a downwardly flaring upper portion leading to the parallel-sided filamentguiding chamber 6.

With the above-described arrangement, the width of each filament formed is determined by the distance separating the teeth of the serrated edge 1a and the thickness of the filament by the thickness of the strip 1. Conveniently, the toothseparation may be between 10- and 40- thousandths and the shim thickness between 4- and 30- thousandths of an inch. The teeth may be square, rectangular or trapezoidal in shape and separated by square, rectangular or trapezoidal spaces.

The material to be extruded is fed to the channel 3 by way of three parallel rows of orifices in the form of circular ducts or bores 10, 11, 12 extending downwardly into the said channel from respective parallel grooves 13, 14, 15 at the bottom of a shallow longitudinal manifold cavity 16 formed in the upper part of the body 4. The outlet ends of the ducts 10, 11, 12 are equally spaced along the channel 3 in one straight line. The entry ends of the ducts 10, 11, 12, however, are staggered, the ducts 1t) and 12 being inclined inwardly and downwardly (FIG- URE 3), while the ducts 11 are vertical. The cavity 16 is covered by a fine-mesh filtering screen 17, suitably of mesh per inch stainless steel, through which the material to be extruded must pass before entering the cavity 16 and the ducts 10-12 leading to the die proper.

The complete assembly illustrated in FIGURE 1 and including the body 4 and base 5 may be inserted in the die head of a conventional ram-type of extruder, in which it may be held in position by means of nuts 18 on studs 19 fixed in the base 5. If the bottom surface of the base 5 and the surface upon which it is mounted have a slight longitudinal inclination, suitably of 2, longitudinal adjustment of the assembly 4, 5 may be arranged to press the body 4 upwardly against the part, located above it, of the die head, a tight joint being ensured by a gasket 20.

As illustrated in FIGURE 4, the die head consists of upper and lower parts 21, 22 secured together by bolts which are not shown. The die assembly is held against the upper part 21 by means of studs 23 screwed into the lower part 22 and arranged to support the base 5 through a frame plate 24. As described above, the die assembly is adjusted longitudinally and tightened by the nuts 18, which act by way of end cheeks 25. The assembly can thus be quickly introduced into and secured in the head. The above mentioned inclination has been shown exaggerated in FIGURE 4.

The serrated shim strip 1 can be easily and cheaply produced by conventional serra-ting means, for instance by punch and die. The cost of replacement is therefore small. The work of disassembly and reassembly of the die with a new strip 1 can be carried out very quickly. Depending on the dimensions of the serrations, filaments can be produced within a wide range of sizes and proportions.

The following dimensions are given by way of example for the case of the extrusion from a reconstituted tobacco composition of filaments, 20-thousandths of an inch Wide and 4-5-thousandths of an inch thick, intended to resemble natural tobacco leaf cut at 50 cuts per inch. The shim strips 1, 2 were 4-thousandths of an inch thick and the serrated edge 1a of the strip 1 had teeth 60 thousandths of an inch wide and SO-thousandths deep, separated by rectangular gaps ZO-thousandths of an inch wide. The edges of the lips 7a of the bars 7 were about 4 th inch thick. In this example, the diameter of the feed ducts 3 -12 was th inch. The die body 4 was about 9 inches long,

I claim:

1. A die for the extrusion of plastic material comprising a die channel, means for supplying the material to said channel, and die slits formed by serrations at one edge of a thin metal sheet disposed in replaceable manner on one side of said die channel.

2. A die according to claim 1, comprising a supporting member, a metal strip, constituting said thin metal sheet, in an edge portion of which said slits are formed and which is bent over a lip of said supporting member.

3. A die according to claim 1, wherein the material is fed to said die channel 'by way of a plurality of rows of orifices opening into said channel.

4. A die according to claim 1, wherein the material is fed to said die channel by way of a plurality of ducts communicating between a manifold cavity in one side of a die body and the die channel in the opposite side of said body, the outlet ends of said ducts being in one straight line, whereas their entry ends are staggered.

5. A die according to claim 1, wherein a filtering screen is provided in said material-supplying means.

6. A die according to claim 1 and further comprising means for mounting it in a die head, which means comprises a device for adjusting said die longitudinally upon longitudinally inclined surfaces, so that said die can be brought tightly against said head by such longitudinal adjust'ment.

7. A die assembly for the extrusion of a plastic material so as to form filaments thereof, said die assembly comprising a body adapted to be supported by a die 'head, said body having a longitudinal channel formed therein,

means on said body for supplying said plastic material to said channel, a replaceable metal sheet mounted on said body and disposed adjacent said channel, said sheet having serrations formed along an edge so as to define die slits which form the filaments as the plastic material passes therethrough.

8. A die assembly for the extrusion of a plastic material so as to form filaments thereof, said die assembly comprising a base member having a slot formed therethrough, a body having a longitudinal channel and passage means connecting a surface of said body with said channel, said body being mounted on said base so that said channel is adjacent to said slot, filament forming means intermediate said channel and slot, said filament forming means including a pair of plate members mounted on said base adjacent said slot, said plate members each having a tapered side wall terminating in a lip portion with said lip portions substantially abutting one another over and at a central portion of said slot to define an extrusion slot, a replaceable metal sheet mounted on one of said plates and extending into said extrusion slot, and said sheet member having serrations formed along an edge so as to define die slits which form the filaments as the plastic material passes therethrough.

References Cited by the Examiner UNITED STATES PATENTS 2,919,467 1/1960 Mercer 1812 3,019,483 2/1962 Schultheiss 1812 X 3,172,154 3/1965 Martin et al. l812 WILLIAM J. STEPHENSON, Primary Examiner. 

1. A DIE FOR THE EXTRUSION OF PLASTIC MATERIAL COMPRISING A DIE CHANNEL, MEANS FOR SUPPLYING THE MATERIAL T SAID CHANNEL, AND DIE SPLITS FORMED BY SERRATIONS AT ONE EDGE OF A THIN METAL SHEET DISPOSED IN REPLACEABLE MANNER ON ONE SIDE OF SAID DIE CHANNEL. 